In semiconductor fabrication, a CMP process refers to a process of planarizing a surface of a semiconductor wafer by applying a polishing agent-containing slurry thereto, followed by performing an orbital movement, in which rotational and linear movements are combined, under conditions that a polishing pad contacts the wafer surface.
Components of slurries used in the CMP process are mainly divided into polishing particles, which performs physical action, and a compound such as an etchant, which performs chemical action. Thus, a CMP slurry selectively etches an exposed portion of a wafer surface through physical action and chemical action, thereby allowing optimum and wide planarization to be accomplished.
Generally, in a semiconductor process, the CMP process is widely used as a process of forming metal interconnects and plugs or vias of a highly integrated circuit. In such a process, first, a low dielectric film, such as SOG, BPSG, O3-TEOS, USG, P-TEOS, FOX, or the like, is deposited on a wafer or a metal layer and a trench is formed in the low dielectric film through photolithography and dry etching. Next, in order to improve adhesion between the metal layer and the low dielectric film, a barrier layer is deposited using titanium, titanium nitride, tantalum, tantalum nitride, and the like. Next, a conductive material such as tungsten, aluminum, copper, or the like is deposited thereon by filling a pattern for metal interconnects or plugs therewith. Finally, the metal layer is completely removed from the low dielectric film by a CMP process using slurries for metal polishing, thereby forming metal interconnects, plugs, vias, and the like.
Since copper has various advantages in terms of efficiency in high integration and the like, copper is frequently used as a metallic material on a semiconductor wafer and forms a porous oxide layer composed of CuO, CuO2, Cu(OH)2 and the like, which are oxides of Cu and Cu2+, upon a CMP process. However, since copper is more vulnerable than a silicon material such as tetraethoxysilane (TEOS) or other materials such as tungsten despite a good polishing rate, copper is likely to suffer from scratching, and particularly, can cause a problem upon photolithography subsequent to a polishing process due to a phenomenon in which foreign substances such as components of a polishing slurry, oxide generated during the polishing process, and the like penetrate into a copper oxide layer through holes of the porous film.
In order to solve such problems, one or more complexing agents or chelating agents are generally added to a CMP slurry for polishing copper interconnects so as to allow chelation or complexation of Cu+ and Cu2+ ions in a copper oxide layer such that the copper oxide layer can be reinforced through removal of holes due to porosity of the film, thereby preventing problems due to penetration of foreign substances during a CMP process. Examples of such additives include imidazole compounds, such as triazole, benzotriazole and the like, and carboxyl group-containing compounds.
However, the polishing rate in the CMP process is deteriorated due to reinforcement of the copper oxide layer, and as a result, there occur problems such as erosion, dishing and the like due to over-polishing caused by increased polishing time. This cause an increase in fabrication costs due to deterioration in yield and productivity upon semiconductor fabrication.